The use of preforms or prepegs in the manufacture of composite materials is well known in the art. In these preforms, strengthening materials such as fibers, whiskers, particulates or the like are incorporated with matrix materials in a form for subsequent processing into fiber reinforced composite materials.
U.S. Pat. No. 5,279,879 to Takezawa et al. disclose a hybrid prepreg containing carbon fibers and at least one other reinforcing fiber. The reinforcing carbon fibers and foreign fibers are impregnated in a thermosetting matrix resin such as an epoxy. The sizes of the foreign fibers and reinforcing fibers are controlled to improve mechanical strength of the prepeg.
It is also known to make the prepegs or preforms by first forming a slurry of an organic binder and a coarse powder. The slurry is then applied uniformly to a fiber containing surface using a doctor blade set at a desired height above the surface. In other prior art processes, a powder, binder and solvent form a slurry which is squeezed onto a moving tape and cured. The fiber material for use in the composite material is then pressed into the tape surface.
Drawbacks associated with these prior art techniques include damage to the fibers and fiber misalignment due to the coarseness of the powders used when mixed with an organic binder. When using a doctor blade, the coarse powders are often dragged by the blade which can interfere with the alignment and spacing of the fibers. In addition, using a slurry as an application media makes it difficult to control the mass per unit area for the composite material preform.
When using the coarse powder-containing slurry, the slurry components can break down the adhesive used to keep the fibers in place during slurry application. Breakdown of the adhesive retaining the fibers in place can cause misalignment of the fibers and an adverse effect on the mass per unit area for the preform material.
In view of the deficiencies in these prior art processes, a need has developed to provide an improved method for making composite material preforms which permits precise control of the preform mass per unit area variable, is low in cost and avoids disruption of reinforcing material alignment in the preform during its manufacture.
In response to this need, the present invention provides a manufacturing method which permits the application of a dry powder in a controlled manner to a variety of surfaces to form various shapes, coatings or other types of composite materials. The inventive method eliminates the need for complicated and expensive equipment for formation of slurries or the like for powder application and is readily repeatable when producing stacked or other multiple layers or arrangements of the preforms or prepegs.